This invention relates to turbochargers and internal combustion engine systems including turbochargers.
Prior art of possible relevance includes commonly assigned U.S. Pat. No. 3,740,170, issued June 19, 1973 to Miller; and the present invention is an improvement on the invention disclosed therein.
Turbochargers are frequently employed in connection with internal combustion engines for compressing combustion air prior to its use by the engine. Typically, exhaust gases from the engine are conveyed to the turbocharger to provide the motive force for compression of the combustion air. As a consequence, the turbocharger housings are subjected to elevated temperatures of the exhaust gases requiring provision for the cooling of bearings to prevent premature failure due to thermal deterioration.
The above identified Miller patent illustrates one such construction wherein lubricating oil is directed to the bearing for the bifold purpose of lubricating and cooling the same. The Miller approach is quite satisfactory for its intended purpose in most installations. However, where the pump for the oil is engine driven and where the turbocharger runs excessively hot due to elevated exhaust system temperature or is located in a cover for fire insulation and/or noise suppression, premature bearing failure and/or turbine end oil seal failure and/or coking of the oil in the housing may nonetheless result.
In particular, once the engine is turned off, the lubricating oil will no longer be directed to the bearings to cool the same. At the same time, residual heat in the turbine section from exhaust gases will be present and cannot readily escape the turbocharger environment due to the fact that the turbocharger is enclosed in such a cover or the exhaust temperature was so high at shutdown that normal conduction overheats the bearings and seals. As a consequence, the heat of the turbine section will flow to the housing in the area of the bearings and seal and to the bearings and cause coking of the lubricant remaining in the housing and on the bearing surfaces which, in turn, will result in undesirable premature seal and bearing failure.
To avoid such a problem, it has been proposed to provide a cooling system for turbocharges for cooling the turbocharge after the engine has been shut off. Rust, in U.S. Pat. No. 3,827,236, issued Aug. 6, 1974, discloses such a system which includes an auxiliary pump which is controlled by a temperature responsive switch in the turbocharger. After the engine is shut down, and when temperatures are sufficiently high as to cause bearing damage, the auxiliary pump is driven by an electric motor to provide cooling oil until safe temperatures are attained. While the Rust system also works well for its intended purpose, it requires additional equipment in the form of switches, pumps, etc., and also imposes a drain on the battery when the engine is not running.